Various features pertain to directional and/or adaptive antennas. At least one implementation pertains to a method, system, and device for transmitting the same signal to two receivers while reducing antenna pattern distortion.
Directional and/or adaptive antennas are typically used to direct a signal transmission in a desired direction. These types of antennas have many advantages over omni-directional antennas when used in modem communications systems. These advantages occur for both transmission and reception of information-bearing signals. During transmission the directional concentration of radiated energy towards a receiver's location significantly increases the amount of received power per unit of transmitted power. This generally improves the quality of the transmitter-to-receiver link and allows higher rates of information transfer. For constant rate transmissions, this improvement in the underlying link enables a reduction in transmitted power, which results in smaller and cheaper power amplifiers. Directional transmissions also contribute to power economy, which is a key consideration in battery-powered devices. Furthermore, in interference-limited systems the concentration of power towards the intended receiver reduces the interference caused by the transmitter to the rest of the system, hence increasing its overall capacity.
Directional antennas are typically implemented as arrays of weighted antenna elements that produce different patterns depending on the weight vector applied. Generally, a receiver and/or transmitter may apply any weight vector to such weighted antennas. One type of directional antenna is a beam switch antenna that can be thought of as being an array of antennas that can be weighted by a finite predefined set of vectors. These predefined set of vectors typically point the resulting antenna beam towards different spatial directions.
In most modem cellular and/or wireless communication systems there are times when the same information is transmitted from a single point to multiple receivers. This is the case, for example, (a) when broadcast channels are employed from a central base station to several user terminals and/or (b) where a particular user's transmission is demodulated by multiple base stations, for instance during the handoff process when the user's terminal transitions from its currently serving base station towards a new base station. For the reasons previously, stated, it is often desirable to employ antenna arrays in these point-to-multipoint transmissions.
It is often the case that each individual entity (e.g., base station or user terminal) transmits a known reference signal, commonly referred to as “pilot”, in order to facilitate the demodulation process at a receiving end. For example, a user terminal could utilize a given base station's pilot signal to find the weight vector(s) that produces the best antenna pattern for communication with such base station. In this context, one way of accommodating the transmission towards multiple points would be to find out the best antenna patterns to use if it were to transmit individually to each one of the multiple receivers and then attempt to synthesize an overall pattern by the sum of all the individual patterns. This combined pattern would be used for the point-to-multipoint transmission.
In generating an antenna pattern to transmit the same signal to multiple receivers, antenna pattern distortions may arise. That is, by transmitting the same signal to multiple carriers, unwanted transmission distortions and cancellations occur that degrade point-to-multipoint transmissions.